Manufacture of steel



gen.

Patented Dec. 23, 1924.

in. a ail STATEfi mam MANUFACTURE STEEL.

No Drawing.

To all whom it may concern:

Be it known that I, PAUL RICHARD KUnHNmciI, a subject of the King ofEngland, residing at Sheffield, in Yorkshire,

England, have invented certain new and useful Improvements in orRelating to the Manufacture of Steel (for which I filed an applicationfor patent in Great Britain on the 1st July, 1922, No. 18,105); and I'do hereby declare that the following is a full,

clear, and exact description of the same.

This invention relates to the manufacture of steel, its object being toprovide an improved cementation process by diffusion of the hardeningconstituents.

The process according to the present invention is carried out in a fusedsalt bath and comprises the simultaneous diffusion of the threeelements, boron, carbon and nitro- The articles to betreated aremanufactured from iron or steel of the desired composition but with alowerpercentage of carbon than is or would normally be required in thefinished state. They are sus' pended in a bath of fused salts, thebulkof which consists of a relatively inert salt (or mixture) such as bariumchloride or calcium chloride of the kind generally used for the heattreatment of steel. According to the present invention, however,hardening properties are imparted to'the ir0n-or steel by adding to thisrelatively inert salt proportions of other fusible salts containingboron, carbon and nitrogen. Different salts in which one or more ofthese three elements are combined may be used according to circumstancesand their proportions may vary. For example to provide mild steel (0.15carbon) articles with a skin 40 which may be hardened sufficiently toscratch glass a bath may be used consisting of 95% of barium chlorideand 5% of calcium borate, potassium carbonate and potassiumferro-cyanide or potassium cyanide in equal proportions by weight.

It appears that the boron first penetrates Application filed June 2a,1923. Serial No. 648,858.

or coke may be used, and it is. found that articles suspended orimmersed in the mixture of fused salts according to this invention areconverted very much more rapidly than by any known cementation process.In addition to the case-hardening effect, a. diffusion and conversion toa very much greater depth also takes place.

What I claim is 1. The method of imparting hardening properties to ironor steel by suspending it in a bath of fused salts the bulk of which isrelatively inert and is mixed with a proportion of other fusible saltscontaining boron, carbon and nitrogen, substantially as specified.

2. The method of im arting hardening properties to iron or stee bysuspending it in abath of fused salts consisting of about 95% of bariumchloride and of about 5% of calcium borate, potassium carbonate andpotassium ferro-cyanide or potassium cyanide in substantially equalproportions,"substantially as specified.

3. The method of imparting hardening properties to iron or steel bysuspending it in a bath of fused salts consisting of about of a mixtureof barium chloride and calcium chloride and of about 5% of calciumborate, potassium carbonate and potassium ferro-cyanide or potassiumcyanide in substantially equal proportions, substan-v 86 tially asspecified.

In testimony whereof I hereunto afiix my signature.

PAUL RICHARD KUEHNRICH. Witnesses:

ARTHUR H. GREENWOOD, HAWTHORN ULRIoH'r.

